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FreeBSD-EN-19:06.dtrace                                         Errata Notice
                                                          The FreeBSD Project

Topic:          DTrace incompatibility with SMAP-enabled systems

Category:       core
Module:         dtrace
Announced:      2019-02-05
Credits:        Mateusz Guzik
Affects:        FreeBSD 12.0
Corrected:      2018-12-19 23:29:44 UTC (stable/12, 12.0-STABLE)
                2019-02-05 17:54:09 UTC (releng/12.0, 12.0-RELEASE-p3)

For general information regarding FreeBSD Errata Notices and Security
Advisories, including descriptions of the fields above, security
branches, and the following sections, please visit
<URL:https://security.FreeBSD.org/>.

I.   Background

DTrace is a dynamic tracing framework that can be used to analyze the kernel
and userspace applications in various ways.

II.  Problem Description

When tracing userspace applications, the kernel component of DTrace may need
to access userspace memory.  With the addition of SMAP support to the amd64
kernel, the kernel is not able to arbitrarily access userspace memory: it
must set a CPU flag to enable access.  The code used by DTrace to perform
such accesses was not updated accordingly.

III. Impact

The problem means that certain DTrace actions do not work on SMAP-enabled
systems.  This does not affect the application being traced.

IV.  Workaround

No workaround is available.

V.   Solution

Perform one of the following:

1) Upgrade your system to a supported FreeBSD stable or release / security
branch (releng) dated after the correction date and reboot.

2) To update your system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +30 "Rebooting for errata update"

3) To update your system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch https://security.FreeBSD.org/patches/EN-19:06/dtrace.patch
# fetch https://security.FreeBSD.org/patches/EN-19:06/dtrace.patch.asc
# gpg --verify dtrace.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/12/                                                        r342267
releng/12.0/                                                      r343783
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-19:06.dtrace.asc>
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